Electron beam uniform intensity control circuit



June 22, 1965 G. G. vn-T, JR., ETAL 3,191,090

ELECTRON BEAl! UNIFORM INTENSITY CONTROL CIRCUIT Filed July 17, 1962 I :2 sheets-sheet 1 June 22, 1955 G. G. vrrT, JR., ETAL 3,191,090

ELECTRON BEAM UNIFORM INTENSITY CONTROL CIRCUIT United States Patent O 3,191,090 ELECTRON BEAM UNIFORM IN'I'ENSITY CONTROL CIRCUIT George G. Vitt, Jr., Los Angeles, and Irving Benjamin Merles, Costa Mesa, Calif., assignors to Hughes Aircraft Company, Culver City, Calif., a corporation of Delaware Filed July 17, 1962, Ser. No. 210,404 4 Claims. (Cl. 315-22) This invention relates to a storage tube control circuit and more particularly to means for controlling the intensity of the writing beam of any direct viewing storage tube whose operation is based upon stored electrostatic charges produced by an electron beam impinging on the surface of a dielectric.

A conventional direct viewing storage tube comprises typically, a writing gun, a flood gun, a storage assembly including a storage screen, a collector grid and a phosphor viewing screen. The storage screen is typically a metallic mesh of several hundred holes per linear inch having a very thin film of deposited dielectric material on the writing gun side. The flood gun provides a large well-collimated spray of W-energy electrons which are directed to impinge upon the storage screen. The stored pattern consists of a charge pattern on the dielectric surface of the storage mesh. Generally speaking, where the dielectric surface is positively charged, the flood electrons are permitted to penetrate the mesh and are accelerated to the viewing screen where they produce a bright pattern. Where the dielectric surface is held negative, that is below its cutoff point, the flood electrons cannot penetrate the mesh but are reflected to return to the collector grid. At intermediate potentials only part of the ood beam passes through to the viewing screen, thus producing intermediate or half tone shades.

The brightness of a display written on the viewing screen of a storage tube depends upon the potential of the storage surface relative to that of the ood gun cathode. The potential of the storage surface depends upon the charge density of the storage surface which in turn is dependent upon and is directly proportional to the secondary emission of the surface and to the writing beam current. If the potential of the storage surface exceeds a critical potential, generally in the order of 40 volts relative to the ood gun cathode, the surface potential will rise to the collector potential by virtue of the flood electrons causing secondary emission from the storage surface. This rise in potential of the storage surface may cause its dielectric strength to be exceeded thus producing a breakdown of the storage surface which may propagate across the entire area of the storage surface.

In addition to preventing a breakdown of the dielectric of the storage surface of a direct viewing storage tube, a writing beam intensity control circuit is necessary when presentations such as Lissajous figures are to be displayed at a constant color on two color direct viewing storage tubes or at a constant brightness on monochromatic halftone storage tubes. One method of writing Lissajous gures provides a nonconstant writing speed. If the beam current or beam intensity is not proportional to the writing speed, at each instant of time, the brightness of the stored figure is different from point to point and is, in fact, inversely proportional to the writing speed.

A two color direct viewing storage tube is similar to a monochromatic halftone storage tube except in the nature of the viewing screen and its position relative to the apertures in the mesh of the storage assembly. In a two color direct viewing storage tube the viewing screen may constitute for example a phosphor color dot matrix. One such matrix is made up of a plurality of color dots each comprising a central phosphor dot of one color, such 3,191,090 Patented June 22, 1965 as red, circumscribed by a phosphor ring of another color, such as green. It should be understood that other colored matrixes may be substituted for that described without varying from the scope of the present invention. The color dots are placed on the inner surface of the at portion of the tube envelope so that each of them is coaxial with one of the apertures in the mesh of the storage assembly.

When a uniform negative charge corresponding to the flood gun cutoff potential is placed on the storage surface no flood electrons will penetrate the mesh. As the storage surface is charged in the positive direction through the action of the secondary emission phenomena, produced by the writing gun, a small number of flood electrons penetrate the storage screen and strike the viewing screen. For low values of voltage above the cutoff potential the apertures of the mesh act like electrostatic lenses which cause the trajectory of the penetrating flood electrons to converge and strike the red portions of the phosphor color dot matrix thus producing a deep red display. As the storage surface is charged increasingly positive the action of the tiny electrostatic lenses changes to produce greater divergence of the trajectories of the penetrating flood electrons, thus activating portions of the green phosphor in the dot matrix. This produces a display in varying hues between red and green depending on the divergence of the flood electrons. When charging of the storage surface has proceeded to such a positive point that ood electrons impinge upon all portions of the green phosphor, the resulting color of the display has such a small fraction of red that it appears as almost pure green.

Therefore the color of the display depends upon the degree of divergence of flood electron beam penetrating the storage mesh. This divergence in turn depends upon the electric field in the immediate vicinity of each of the apertures of the mesh. To Write a constant color display it is necessary to maintain this field constant by laying down a uniform charge density in all areas defined by the display geometry. Therefore, in order to write Lissajous figures of constant hue or of a constant monochromatic halftone value with a writing beam having a varying speed, it is necessary to modulate the Writing beam current so that it is proportional to the speed of the beam.

The speed of the electron beam, relative to the storage surface which it strikes, that is, the writing speed, is controlled by the rate of change of the electrostatic fields developed normal to each of the pair of horizontal and vertical deflection plates and is the resultant of the vertical and horizontal velocity components. Since each of the deflection fields has a corresponding potential, the resultant velocity can be expressed as a value which is the square root of the sum of the squares of the voltages proportional to each of the horizontal and vertical deflection voltages. Therefore, the intensity of the writing beam of the writing gun can be controlled as a function of the writing beam velocity by applying the voltage representing the square root of the sum of the squares of the horizontal and vertical deflections to the grid or intensity control element of the writing gun.

It is therefore an object of this invention to provide a means to prevent the charge on the storage surface from reaching a critical potential relative to the flood gun cathode.

It is another object of this invention to provide a means for controlling the intensity of the writing beam as a function of the velocity of the writing beam.

It is a further object of this invention to provide means for cutting off the writing beam when the writing velocity falls to such a low value that damage to the storage surface may result.

It is still another object of this invention to provide means for providing in a storage tube a trace having constant intensity under conditions of nonconstant writing speed.

It is yet another object of this invention to provide means for establishing in a multicolor storage display tube a trace of constant hue under conditions of nonconstant writing speed.

In general, in its preferred form the present invention comprises a system for controlling the instantaneous intensity of the Writing beam current of a direct viewing storage tube having a writing beam generating means and a beam deflection control means, which includes a rst means for deriving from said beam deilection control means, a pair of orthogonally related signals each representative of the displacement of said beam from a normal axial position. A second means coupled with said iirst means for generating a control signal having a magnitude representative of the square root of sum of the square of the instantaneous values of said orthogonally related signals and coupled for applying said control signal to said beam generating means.

Other advantages of the invention will hereinafter become more fully apparent from the following description of the drawings which illustrate two embodiments, and wherein:

FIGURE 1 is a schematic drawing and block diagram illustrating a preferred embodiment of the present invention as applied to a direct viewing storage tube having a cutaway portion showing schematically the electron gun, writing gun, and deflection plates;

FIG. 2 is a block diagram showing diagrammatically the elements of a particular embodiment of the present invention as well as the algebraic form of the output of each of the elements;

FIG. 3 is a schematic circuit diagram of a particular squaring circuit illustrated as one of the blocks in FIG. 2;

FIG. 4 is a graph showing curves representing the output of the sheet beam tube of the squaring circuit of FIG. 3 under varying conditions;

FIG. 5 is a schematic circuit diagram of a particular square root circuit illustrated as one of the blocks in FIG. 2;

FIG. 6 is a schematic circuit diagram of a particular control circuit for the pulse rate frequency of the blocking oscillator illustrated as one of the blocks in FIG. 2;

FIG. 7 is a schematic circuit diagram of a particular squaring circuit representing a second embodiment of the squaring circuit illustrated as one of the blocks in FIG. 2;

FIG. 8 is a graph showing a curve representing the transfer characteristic of the second embodiment of the squaring circuit illustrated as one of the blocks in FIG. 2;

FIG. 9 is a schematic circuit diagram of a particular square root circuit representing a second embodiment of the square root circuit illustrated as one of the blocks in FIG. 2; and

FIG. 10 is a graph showing a curve representing the transfer characteristic of the second embodiment of the square roo't circuit illustrated as one of the blocks in FIG. 2.

Referring now to the drawings and particularly FIG. 1, a direct viewing storage tube 10 which operates typically in conjunction with an intelligence signal source 12, and a dellection voltage generator 14, includes an evacuated envelope which consists of an enlarged cylindrical portion 17 having a neck portion 18 at one extremity and a llat and transparent portion 20 at the other extremity. An electron gun 21 comprising a cathode 27 and a control grid 28 is provided for producing and controlling an electron beam of elemental crosssectional area. Scanning of the electron beam is accomplished by deection members illustrated as horizontal deflection plates 22 and vertical dellection plates 24 for directing the electron beam towards selected elemental areas of a storage screen, not shown. It is of course to be understood that other deilection means may be used. A ilood gun 25 produces a broad beam of electrons, directed towards the storage screen, for supplying the display target with such energizing electrons as are permitted to pass through the storage target.

In operation, the cathode 27 is maintained at a potential of the order of 2000 volts negative with respect to ground by means of a connection to the negative terminal of a source of potential illustrated as a battery 30 the positive terminal of which is connected to ground. In the normal operation of a direct viewing storage tube intensity grid 28 is maintained at an adjustable potential of the order of 50 volts negative with respect to the cathode 27. This may be accomplished by means of a source of variable potential such as a battery 32 being connected between the intensity grid 28 and the cathode 27 in series with a resistor 31. However, in accordance with the present invention, a writing beam control circuit 34 is additionally included in series between the resistor 31 and the grid 28 such that further modulation of the writing beam may be provided by the control circuit. However, it should be understood that modulation of the writing beam can also be produced by the intelligence signal source 12 alone or operating in combination with the writing beam control circuit 34. When the intelligence signal source 12 is used for modulation it is connected to the writing beam control circuit 34 through a capacitor 35.

The deilection voltage generator 14 develops conventional horizontal and vertical dellection voltages which may be synchronized in any desired manner with the intelligence signal or with one another. The horizontal and vertical dellection voltages are impressed on the horizontal and vertical deflection plates 22, 24, respectively, by means of appropriate connections thereto.

Referring now specifically to FIG. 2, the output voltages of both a horizontal deflection voltage squaring circuit 37 and a vertical deflection voltage squaring circuit 37a are applied to a summing device or circuit 38, which is typically a conventional analogue operational feedback amplifier adder such as a K2-X type as manufactured by G. A. Philbrick Researcher, Inc. The output voltage of the summing device 38 is applied to a square root circuit 40, the output voltage of which is applied to a relaxation oscillator 42 which is typically a conventional blocking oscillator such as a Z-90015 type as manufactured by Engineered Electronics Co. The voltage pulses developed by the oscillator 42 are summed with a writing gun negative bias potential 41, to be described later, and when appropriate the intelligence signal 12 by a summing device 44, which is typically a conventional analogue operational feedback amplier adder such as that above mentioned and applied through a control circuit 45 to the grid 28 of the writing gun 21.

Referring now to FIG. 3, the squaring circuits 37 and 37a of the rst embodiment may be identical, each including a pair of triode electron discharge devices illustrated as a dual triode 46 connected as a pair of conventional ditferential ampliers wherein the cathode of each triode is connected through a common resistor 47 to the negative terminal 48 of a source of potential. The anode of each triode is supplied with an operating potential through a load resistor 50, and the control grid 51 of one triode is supplied with a signal potential and the control grid 51a of the second triode is connected to ground. The output voltage of the dual triode 46 is coupled by means of a coupling element, such as a conventional neon tube 52, typically of a NE-S 1 type, to one of the deflection plates of a conventional sheet beam tube 53 such as a 6AR8 type which includes a rst grid element 54 connected through a grid resistor 55 to the positive terminal 56 of a source of potential and a second grid element 57 connected through a control circuit comprising a capacitor 58, a variable resistor such as bias control potentiometer 59 and a xed resistor 60 to the negative element 61 of a source of potential. While the potential on the first grid 54 remains a constant positive value, the negative potential on the second grid 57 can be adjusted by the manipulation `of the potentiometer 59 to control the voltage output of the sheet beam tube 53. The voltage level changing devices have been shown and described as the neon tubes 52; however, it should be understood that a constant voltage level device such as a Zener diode may be substituted therefor without varying from the scope -of the present invention.

As best seen in FIG. 4 the characteristics of the sheet beam tube 53 are such that the current Ip through the load resistor 62 is a minimum when the electron beam moving between the cathode and anode of the tube is undeflected, and that this current increases as the square of the deflection voltage ED provided by the dual triode 46. Therefore, it can be seen that the squaring circuit 37 and 37a constitute perfect squaring devices because regardless of the polarity of the voltage applied to the first grid 51 of the dual triode 46 and the corresponding deflection of the electron beam of the sheet beam tube 53 the direction of the current Ip through the load resistor 62 does not change.

To enable the sheet beam tube 53 to be coupled to the summing circuit or device 38, a coupling element, such as a conventional neon tube 63, typically of a NE-Sl type, is interposed in series with the output of the sheet beam tube 53 and the input to the summing circuit 38. The voltage level changing device has been depicted in FIG. 3 as the conventional neon tube 63; however, it should be understood that a constant voltage level device such as a Zener diode may be substituted therefor without varying from the scope of the invention.

To extract the square root of the summation of the horizontal and vertical deiiection voltages the voltage output of the summing device 38 is supplied to the square root circuit 40 which in a preferred embodiment comprises, as shown in FIG. 5, a xed resistor 64, and a variable resistor or potentiometer 65 connected in series with the fixed resistor 64, Vand a conventional semiconductor diode 66 connected between one side of the potentiometer 65 and ground. Because of the volt ampere transfer characteristics inherent in the semiconductor diode 66 and the constant current characteristics provided by the potentiometer 65 and the fixed resistor 64 the current output of the circuit 40 is proportional to the square of the voltage applied to it.

Referring again to FIG. 2, the output voltage of the square root circuit 40 is applied to a relaxation oscillator 42 which is typically a conventional blocking oscillator and will hereafter be described as such. However, it should be understood that other types of relaxation oscillators such as a multivibrator may be used without varying from the scope of t-he invention. The form of the output voltage of the blocking oscillator 42 is a series of pulses of constant amplitude and duration and at a variable pulse repetition frequency. It is the characteristics of a blocking oscillator that the pulse repetition frequency of the output voltage pulses is a function of the amplitude of the control voltage applied to the oscillator. Therefore, as the square root of the sum of the squares of the deflection voltages increases the pulse repetition frequency of the output voltage of the blocking oscillator also increases.

To prevent breakdown of the dielectric of the storage surface when the velocity of the Writing beam falls below a predetermined value the output pulse of the blocking oscillator 42 is cut off by the adjustment of a typical RC biasing circuit (not shown) built into the oscillator. As shown in FIGS. l and 2 when the oscillator voltage pulse output is cut off, that is the writing beam control circuit output is zero, the control grid 28 of the writing gun will be biased negatively by the voltage developed by the battery 32 across the resistor 31. This negative potential cuts off the writing beam until the positive voltage pulse output of the blocking oscillator 42 overcomes the negative biasing potential and places a positive potential on the control grid 28.

To prevent the writing of a series of dots on the viewing screen, when the pulse repetition frequency of the blocking oscillator 42 is low, that is the square root of the sum of the squares of the defiection voltages is low, a control circuit 45 operates on the output voltage of the blocking oscillator 42. This is necessary because at the maximum writing speed of the writing gun the pulse repetition frequency may not be high enough to turn the beam on and off before it has traversed its own diameter. Referring to FIG. 6 the control circuit 45 comprises a standard RC low-pass filter detector circuit including a capacitor 67 and a resistor 68, and a conventional diode 69 in parallel with the filter elements. To retain a continuous display on the viewing screen, when the blocking oscillator output voltage is zero, that is during the interpulse time, the capacitor 67 will discharge through the resistor 68 to retain a positive bias on the control grid 28.

Referring now to FIGS. 7 and 9 there is illustrated a second embodiment of the squaring circuit 92 and a second embodiment of the square root circuit 94. The second embodiment of the squaring circuit 92 comprises a conventional analogue operational feedback amplifier 80, typically such as a KZ-X type, including in series With it a gain control circuit comprising a first resistor 81 and a second resistor 82, a conventional semiconductor diode 83 and a battery 84 in parallel with the first resistor 81 and in parallel with it a feedback resistor 85 in parallel with the feedback amplifier 80. The second embodiment of the square root circuit 94 comprises a conventional analogue operational feedback amplifier 86 typically of a K2-X type including in parallel with it a gain control circuit constituting a feedback circuit which includes a battery 87, a conventional semiconductor diode 88 and a second resistor 89 in parallel with a feedback resistor 90 and a first resistor 91 in series with the feedback amplifier 86.

For clarity of description of the operation of the second embodiment `of the squaring circuit 92 along with the graph of its transfer characteristics as shown in FIG. 8, and the second embodiment of the square root circuit 94 along with the graph of its transfer characteristics as shown in FIG. 10, the potential of the batteries 84 and 87 will be assumed to have a Value of 2.6 volts. It should be understood that while specific values of voltage have been chosen, these Values are not critical and that other values of voltage may be substituted therefor without varying from the scope of the present invention.

Referring first to FIG. 7, as the input voltage E, (that is the X or Y deflection voltage) increases from zero to +26 volts the gain of the amplifier 80 is low because of the effect of the feedback resistor 85, the first resistor 81, and the nonconductivity of the diode 83 due to the back bias of 2.6 volts placed on it by the battery 84. After the input voltage Ei vincreases to ,-{-2.6 volts, the diode 83 becomes conductive and places the second resistor 82 in parallel with the first resistor 81 to increase the gain of the amplifier 80. This can be seen from FIG. 8, the gain of the amplifier remains at a relatively low value until the input voltage El exceeds the first break point at 2.6 volts; thereafter, the slope of the curve increases approximately exponentially until at a representative point the output Voltage Eo has a value of 64 volts when the input voltage Ei is 8 volts.

While the operation of the squaring circuit of FIG. 7 has been described with a single gain control circuit it should be understood that other branches similar to that comprising the second resistor 82, the diode 83, and the battery 84 may be connected in parallel with this branch to further control the gain of the squaring circuit.

Referring now to FIG. 9 the second embodiment of the square root circuit 94 operates similar to the operation of the second embodiment of the squaring circuit 92, however, as the input voltage increases to the first break point determined by the potential of the battery 87, here assumed to be 2.6 volts, the gain of the amplifier 86 is relatively high because the resistor 89 remains out of the circuit due to the back bias of the diode 88 by the battery 87. As the input voltage increases to 5.2 volts the diode 88 begins to conduct placing the first resistor 89 in parallel with the feedback resistor 90 and decreases the gain of the amplifier 86. Here, again a single gain control circuit has been described. However, it should be understood that additional branches such as the battery 87, the diode 88, and the first resistor 89 can be placed in parallel with this branch for additional gain control of the amplifier 86.

The operation of the square root circuit of FIG. 9 can be seen from its transfer characteristic depicted in FIG. 10. As the input voltage E, increases from zero to 5.2 volts the gain of the amplifier 86 remains relatively high; however, when the input voltage E1 exceeds 5.2 volts the gain of the amplifier 86 decreases due to the conduction of the diode 88 causing the slope of the curve to decrease until at a representative point the output voltage E has a value of 8 volts when the input voltage El is 64 volts.

Although the now preferred embodiments and methods of the present invention have been illustrated and described it is to be understood that the invention need not be limited thereto for its is susceptible to change in form, detail and application within the scope of the appended claims.

We claim:

;1. A system for controlling the instantaneous intensity of the writing beam current of a direct viewing storage tube having beam intensity control means and beam deection members comprising:

means coupled with said deflection members for providing beam deection control signals;

first circuit means coupled with said last named means and including an amplifying means and a deflectable beam electron discharge means connected in cascade for providing an output signal having a magnitude representative of the square of the magnitude of said deflection control signals;

second circuit means coupled with said discharge means for providing a signal representative of the square root of the sum of the squares of said deliection control signals;

and control signal means connected to said second circuit means for applying a control voltage to the beam intensity control means, said control signal means including an oscillator means for developing under predetermined conditions a control signal of constant amplitude having a repetition frequency proportional to the magnitude of the square root signal and a biasing means for maintaining said intensity control means inoperative until said control signal has reached said predetermined magnitude. whereby the current of the writing beam is controlled as a function of the velocity of the Writing beam.

2. A system for controlling the instantaneous intensity of the writing beam current of a direct viewing storage tube having beam intensity control means and deflection members comprising:

signal generating means coupled with said deflection members for providing beam deflection control signals;

first circuit means coupled with said last mentioned means for providing a signal having a magnitude representa-tive of the square of the magnitude of said deflection signals, including an amplifying means and a sheet beam tube having a pair of deflection plates coupled with said amplifying means;

second circuit means coupled with said first circuit means for providing a signal having a magnitude representative of the square root of the sum of the squares of the deliection control signals, including a diode and means to lprovide a constant current characteristic for said second circuit means;

and control signal means connected to said second circuit means for applying a control voltage to said beam intensity control means under predetermined conditions, said control signal means including a blocking oscillator adapted to develop when said square root signal has reached a predetermined magnitude a control signal having a duty cycle proportional to the magnitude of the square root signal, and a biasing means for maintaining said intensity control means inoperative until said control signal has reached a predetermined magnitude and a pulse repetition frequency control means adapted to turn the lwriting beam on and off before it has moved a distance equal to the diameter of the beam, whereby the current of the writing beam is controlled as a function of the velocity of the Writing beam.

3. A system for controlling the instantaneous intensity of the Writing beam current of a direct viewing storage tube having beam intensity control means and beam deflection members comprising:

means coupled with said deflection members for providing beam deflection control signals;

first circuit means connected to said last mentioned means for providing a signal representative of the sum of the squares of said deflection control signals, `said means including an amplifying means and a circuit means to control the gain of said amplifying means;

second circuit means connected to said first circuit means for providing a signal representative of the square root of the sum of the squares of said deection signal, said means including an amplifying means and a circuit means to control the gain of said ampliying means; and means connected to said second circuit means for applying a control voltage to the beam intensity control means, said means including an oscillator means for developing under predetermined conditions a control signal of constant amplitude having a repetition frequency proportional to the magnitude of the square root signal and biasing means for maintaining said intensity control means inoperative until said control signal has reached said predetermined magnitude,

whereby the current of the writing beam is controlled as a function of the velocity of the writing beam.

4. A system for controlling the instantaneous intensity of the writing beam current of the Writing beam of a direct Viewing storage tube having beam intensity control means and beam deflection members comprising:

means coupled with said deflection members for provid-v ing beam deflection control signals;

first circuit means connected to said last mentioned means for providing a signal representative of the sum of the squares of said deflection control signals, said means including an amplifying means, a feedback resistor in parallel with said amplifying means, a first resistor in series with said amplifying means and a gain control circuit in parallel with said first resistor for increasing the gain of said amplifying means under predetermined conditions;

second circuit means connected to said first circuit means for providing a signal representative of the square root of the sum of the squares of said deection signals, said means including an amplifying means, a feedback resistor in parallel with said amplifying means, a resistor in series with said amplifying means and a gain control circuit in parallel with said feedback resistor;

and means connected to said second circuit means for applying a control voltage to said beam intensity 9 10 control means under predetermined conditions, said References Cited by the Examiner means including a blocking oscillator adapted to de- UNITED STATES PATENTS velop when said square root signal has reached a 2 747 085 5/56 Gardner et al 328 144 predetermined magnitude a control signal having a 2860284 11/58 McKm 315 22 duty cycle proportional to the magnitude of the 5 3055588 9/62 Ratz "235 193 square root signal and a biasing means for maintaining said intensity control means inoperative until said OTHER REFERENCES control signal has reached a predetermined magni- Chance et al.: Waveforms, M.I.T. Radiation Lab. Series,

tude and a pulse repetition frequency control means McGraw-Hill, 1949, page 692, QC 601C5. adapted to turn the writing beam on and off before it 10 Soroka, W. W.: Analog Methods in Computation and has moved a distance equal to the diameter of the slmulatlll, McGraw-H111, 1954, Pages 64, 65, QA 76-456- beam,

whereby the current of the writing beam is controlled as DAVID G' REDINBAUGH Pnmary Examiner a function of the velocity of the writing beam. ROBERT SEGAL, Examiner.

NITED STATES PATENT OFFICE CERTIFICATE F CORRECTION Patent No. 3,191,090 June 22, 1965 George G. Vitt, Jr., et al.. l

It is hereby certified tha-t error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Co1umn 6, line 29, strike out "in parallel with it"; column 7, line 56, for "magnitude." read magnitude,

Signed and sealed this 18th day of January 1966.

(SEAL) Attest:

ERNEST W.SW1DER yEDWARD J. BBErIrJER Attesting Officer Commissioner of Patents NITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3,191 ,090 June 22, 1965 George G. Vitt, Jr. et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 6, line 29, strike out "in parallel with t"; column 7, line 56, for "magnitude." read magnitude,

Signed and sealed this 18th day of January 1966.

(SEAL) Attest:

ERNEST W. SWIDER rEDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. A SYSTEM FOR CONTROLLING THE INSTANTANEOUS INTENSITY OF THE WRITING BEAM CURRENT OF A DIRECT VIEWING STORAGE TUBE HAVING BEAM INTENSITY CONTROL MEANS AND BEAM DEFLECTION MEMBERS COMPRISING: MEANS COUPLED WITH SAID DEFLECTION MEMBERS FOR PROVIDING BEAM DEFLECTION CONTROL SIGNALS; FIRST CIRCUIT MEANS COUPLED WITH SAID LAST NAMED MEANS AND INCLUDING AN AMPLIFYING MEANS AND A DEFLECTABLE BEAM ELECTRON DISCHARGE MEANS CONNECTED IN CASCADE FOR PROVIDING AN OUTPUT SIGNAL HAVING A MAGNITUDE REPRESENTATIVE OF THE SQUARE OF THE MAGNITUDE OF SAID DEFLECTION CONTROL SIGNALS; SECOND CIRCUIT MEANS COUPLED WITH SAID DISCHARGE MEANS FOR PROVIDING A SIGNAL REPRESENTATIVE OF THE SQUARE ROOT OF THE SUM OF THE SQUARES OF SAID DEFLECTION CONTROL SIGNALS; AND CONTROL SIGNAL MEANS CONNECTED TO SAID SECOND CIRCUIT MEANS FOR APPLYING A CONTROL VOLTAGE TO THE BEAM INTENSITY CONTROL MEANS, SAID CONTROL SIGNAL MEANS INCLUDING AN OSCILLATOR MEANS FOR DEVELOPING UNDER PREDETERMINED CONDITIONS A CONTROL SIGNAL OF CONSTANT AMPLITUDE HAVING A REPETITION FREQUENCY PROPORTIONAL TO THE MAGNITUDE OF THE SQUARE ROOT SIGNAL AND A BIASING MEANS FOR MAINTAINING SAID INTENSITY CONTROL MEANS INOPERATIVE UNTIL SAID CONTROL SIGNAL HAS REACHED SAID PREDETERMINED MAGNITUDE. WHEREBY THE CURRENT OF THE WRITING BEAM IS CONTROLLED AS A FUNCTION OF THE VELOCITY OF THE WRITING BEAM. 